Magnetic field sensors which determine a magnetic field with respect to a plurality of measuring axes must normally be calibrated using a complex measurement technique during manufacturing. The calibrating procedure may be very complex and costly. In particular when the magnetic field sensor is very precise, for example when it is intended to measure and record the earth's magnetic field, a complex calibrating procedure using a complex measurement technique is required.
Apart from manufacturing tolerances, instances of interference of such a magnetic field sensor may also be a function of an environment of the sensor at the point of use, so that the calibration during manufacture is not adequate. For example, soft magnetic and/or magnetized objects or current-carrying conductors passing close to the magnetic field sensor may falsify the determined magnetic field. When the magnetic field sensor is used, for example, in a mobile telephone or a portable computer, such interference is practically unavoidable.
U.S. Pat. No. 7,275,008 describes a method for compensating measurement errors of three-dimensional magnetic field measured values, a geometric body having a number of recorded measured values lying on its surface being determined. Parameters which define a deviation of the shape of this body from the geometric reference figure of a sphere are determined. The parameters are used for plotting recorded measured values on calibrated measured values.
An object of the present invention is to provide a calibration method for a three dimensional magnetic field sensor requiring low computational complexity, so that it may be used as efficiently as possible in a mobile device.